Probing the Depths of Crater Lake: A Century of Scientific Research by Douglas Larson
In August 1912, during a yearlong survey to determine the chemical composition of Oregon lakes and rivers, Walton Van Winkle and N. M. Finkbinder of the USGS stopped briefly at Crater Lake to obtain a water sample for chemical analysis. Based on this first analysis of Crater Lake water, which was collected from a depth of six feet about one mile from shore, Van Winkle postulated that the lake’s waters were initially acidic but eventually were neutralized by reaction with alkaline rock material that lined the caldera. Nevertheless, despite the preponderance of alkaline rock, lake waters remained slightly acidic. Van Winkle called this a “remarkable circumstance” and attributed it to the lake’s relatively high concentrations of chloride and sulfate. He concluded that the source of the chloride was rain and snow and that sulfate was produced by the dissolution of sulfur deposits in the bottom of the caldera.
|National Park Service ranger-naturalists are show here planting fish in Crater Lake in September 1932. Photo courtesy of the National Park Service|
During the summer of 1913, fishery biologists of the U.S. Bureau of Fisheries made other important discoveries about the unusual limnology of Crater Lake. George Kemmerer, J. F. Bovard, and W. R. Boorman were the first scientists to collect and identify samples of the lake’s microscopic plant and animal life. They collected water samples from the lake’s surface to its bottom with a deep-water brass sampling apparatus. This device, once filled, was retrieved from depth and hauled into the boat, where the biologists poured the water sample through a net capable of catching plankton as small as 76 microns (0.076 millimeters) in diameter. Microscopic plants, or phytoplankton, were found at depths reaching 650 feet. Two major types were identified: diatoms, which are single-cell plants with cell walls comprised of silica, and filamentous green algae. They also found microscopic animals, or zooplankton, including rotifers and “several” crustacean species, the most common of which were water fleas, identified as Daphnia pulex. Based on stomach analyses of fish caught in the lake, the three biologists determined that water fleas were a major food source for the lake’s rainbow trout.